1. Field
The present invention relates generally to communication, and more specifically to techniques for interleaving data in a communication system.
2. Background
In a communication system, a transmitter typically encodes a packet of traffic data to generate a packet of code bits, interleaves or reorders the code bits, and modulates the interleaved bits to generate modulation symbols. The transmitter then processes and transmits the modulation symbols via a communication channel. The data transmission is degraded by impairments in the communication channel, such as thermal noise, interference, spurious signals, and so on. A receiver obtains a distorted version of the transmitted modulation symbols.
Encoding and interleaving allow the receiver to recover the transmitted traffic data in the presence of degradations in the received symbols. The encoding may include error detection coding that allows the receiver to detect for errors in the received traffic data and/or forward error correction (FEC) coding that allows the receiver to correct for errors in the received traffic data. FEC coding generates redundancy in the coded packet. This redundancy allows the receiver to recover the transmitted traffic data even if some errors are encountered during transmission. The interleaving reorders or shuffles the code bits in the packet so that code bits that are near each other are separated in time, frequency, and/or space during transmission. If a burst of errors occurs during transmission, then these errors are spread apart after the de-interleaving at the receiver, which improves decoding performance.
An interleaver is often designed to achieve good performance for packets of a particular size. (The term “size” and “length” are synonymous and are used interchangeably herein.) If the communication system supports multiple packet sizes, then a different interleaver is often designed and used for each packet size. The use of multiple interleavers for different packet sizes can complicate the interleaving at the transmitter and the de-interleaving at the receiver, especially if the system supports a wide range of packet sizes.
There is therefore a need in the art for techniques to efficiently perform interleaving for packets of different sizes.